Google’s and Facebook’s preparations for the General Data Protection Regulation have caused a headache for marketers that relied on the platforms for ad targeting.

Marketers said they now struggle to comprehensively measure their targeting across the platforms within their own data management platforms, forcing some to turn to third-party measurement partners and others to be complacent with piecing together the data they do have strictly within Google and Facebook. Say a marketer ran a campaign across Google and Facebook. Now, they can no longer see if an ad reached the same person on Google as well as on Facebook.

Google’s changes to its data sharing came ahead of the GDPR enforcement deadline on May 25. The Google DoubleClick IDs once let buyers transfer files of DoubleClick impressions from across Google’s ad products from Google’s DoubleClick Campaign Manager to their own DMPs. At the end of April, Google disallowed ad buyers from using the Google DoubleClick ID to export data.

Facebook made a similar move, citing the need to protect people’s privacy. As a result, their view tags are no longer usable by other platforms such as Google’s DoubleClick. Already, some marketers’ say that within their DMPs, they cannot measure views across their Facebook buys, only clicks.

Not only can marketers and agencies no longer track whether an ad reached someone on Google, but not on Facebook, and vice versa, the changes also complicate the ability to see if their ads are being seen by new audiences or people who have already seen the ads on another platform.

“This evolution is creating issues for marketers and agencies alike,” said one agency executive, speaking anonymously for fear of retribution by the platforms. “In some ways, it’s not surprising. Walled gardens want to make their walls taller because it benefits them and protects them against GDPR, but it makes achieving what all brands wants to achieve — one view of the customer, one view of the journey, a comprehensive understanding of how effective their marketing is — more challenging.”

Brandon Solis, strategy director at R/GA, said that being able to use the DoubleClick ID and Facebook view tags within their DMPs created efficiencies for marketers. “We knew we could guarantee an impression some way,” said Solis. “That was the benefit of audience sharing: If we don’t capture you somewhere, we can see that we’ve captured them somewhere else. Now, there’s not that guarantee.”

To cope, marketers are adopting more third-party measurement companies. One marketer at an international company, speaking anonymously, said it was now working with Amazon and Nielsen to target its ad buys across all platforms since it can no longer do so through its DMP.

Agency executives said GDPR has only strengthened walled gardens and had the effect of pitting one tech giant against the other. Now, to measure accurately, marketers will have to tailor their campaigns to each individual platform or just go all-in on one, Solis said.

“This just shows how competitive the data and the measurement is and how the platforms are all staking their claim to that,” said another agency executive, who asked for anonymity. “It’s a battle between Facebook and Google.”